The problem isn't in the cost of repairing an old vehicle, it's the ability of repairing an old vehicle.
I had a 1988 4Runner that was in such bad shape, it was totaled twice (deer). I'm not a mechanic or a body shop person, but I pieced it back together both times. I drove it to 189,000 miles before upgrading to a new truck. That was in 2002 that I sold it and I know it was still on the road about 2 years ago (I sold it cheap).
I have a 1994 Honda Civic right now. I paid $20 for the car

. It has a blown head gasket on it's 185,000 miles. A call to the shop netted me a repair bill of $800-900. It's a simple matter of disconnecting things and reconnecting them afterwards. It's half ripped down in the driveway now and will cost me $100 to fix.
Repair shops are a major rip-off. They bill by what a book tells them how long it will take, then they take shortcuts to get the job done in a tenth of the time.
Example, I needed a ball joint replaced in my old 4Runner. My brother-in-law working for a dealership garage had me come up on the weekend so we could use the lift. He looked up the job and it was a 3 hour job. At $70/hour, that would have been $210 in just labor. The book stated to remove the hubs, remove the axle, remove the lower a-arm, etc. etc. We removed the tire, unbolted the 4 bolts on the ball joint, he lifted up the suspension with a pry-bar while I pulled and replaced the ball joint. That 3 hour $210 labor job took us less than 10 minutes.
Repairing a car is easy, even for the girls. With the internet, all it takes is going to a car forum and asking, what's wrong with my car? There you can figure out what's wrong and find how to repair it. All you need for most work is a socket set and some wrenches. It turns just about every $1000 repair into a $100 repair.
I called Toyota once. My starter was out. I had known how to easily and cheaply rebuild it from the internet. I called Toyota and asked for the rebuild kit. Of course, they did not have a rebuild kit and I had to cough up $450 for a remanufactured starter. I got back on the net and asked about the part number for the rebuild kit. 5 minutes later with the actual part number, I called the Toyota parts shop again and asked for the specific part number. "Yeah, the starter rebuild kit, we can get that for you. It will be $11.25" It was the same guy I tried ordering the kit from half and hour before. Picked up the part and in 10 minutes in the driveway, I had the 2 bolts out holding the starter in, 2 bolts holding the starter casing together out, replaced the contacts, a couple of o-rings, and had it all put back together. Saved $438.75 for 10 minutes of my time with a single wrench. Anyone, including the lovelier members of our species, can do that.